Prepregs are resin preimpregnated mats, fabrics or layers composed of unidirectional elementary fibers. For manufacturing fiber components from prepregs, the latter are spread on a mold and the prepregs are caused to adhere to one another by means of heat and pressure. For components of complex geometries the prepregs are trimmed to size before spreading them on the mold.
To protect the prepregs from contamination and damage when they are worked on with trimming tools, the prepregs which can be made of carbon, glass or aramid fiber are provided with protective sheets on both surfaces thereof. When being trimmed to size, the prepregs are held, together with the protective sheets, by mechanical fixing means such as clamps or they are secured on a smooth table by means of negative pressure (suction), where a vacuum is created under the prepreg with its protective sheet. For this purpose, the table is provided with holes or consists of plastic brushes in a very dense arrangement to prevent the necessary suction pressure from being diminished by leakage flows.
The trimming tools are operated automatically or manually, and can be constructed as knives, laser cutters, high-pressure water jets or ultrasonic cutters. In the cutting operation, the prepreg may be cut together with only one of the two protective sheets, with the individual blanked-out prepregs remaining together, or both sheets are cut to produce separate, individual precut parts.
The known procedure for fixing the prepregs in position either requires relatively elaborate mechanical fixing means on the processing tool, or else comprehensive vacuum devices, the latter additionally being susceptible to contamination, where the suction holes may be blocked or the plastic brush seals closed off. Also, the hold-down force diminishes when the prepregs lift off the support, no matter how little.